Adam Gault/Thinkstock(LAS VEGAS) -- As authorities pick apart the life of Las Vegas shooter Stephen Paddock, they have come across one major thread of suspicious behavior: how he handled his money.

Paddock’s recent financial transactions have become a key focus for investigators looking to learn more about the Nevada man and why he launched the deadliest mass shooting in modern U.S. history.

As ABC News first reported on Monday, Paddock recently sent tens of thousands of dollars to someone in the Philippines, where his girlfriend was at the time of the attack, and authorities are still trying to determine who received that money, sources familiar with the matter said.

In the last three years alone, more than 200 reports about Paddock’s activities, particularly large transactions at casinos, have been filed with law enforcement authorities, ABC News was told.

While some of the reports centered around "suspicious activity," many were "currency transaction reports," which casinos are required to file with the Treasury Department when a person withdraws or deposits more than $10,000 in cash.

One law enforcement official noted "currency transaction reports" are "not necessarily suspicious," especially "if you’re a high roller."

The FBI has already briefed some lawmakers about what they’ve found so far as agents dig into Stephen Paddock's past.

"Bottom line, this man was a gambler, but I do not believe there is sufficient evidence to show that he was under stress financially from gambling at the time this incident occurred," Sen. Claire McCaskill, D-Missouri, told ABC News.

Paddock’s longtime girlfriend is originally from the Philippines, and she is believed to have been there when he launched his deadly assault in Las Vegas, killing 59 people and more than 500 others attending a country music festival. She is expected to return to the United States tomorrow.

Check Also

iStock/Thinkstock(NEW YORK) -- The stepmother of a 5-year-old boy who's been missing since Saturday has been arrested, officials announced Wednesday.Wichita police said 26-year old Emily Glass was arrested for child endangerment as they continue to loo...